1. Technical Field
The present invention relates to an improvement on a piezoelectric resonator element and a piezoelectric device including the piezoelectric resonator in its package or case.
2. Related Art
Piezoelectric devices, including a piezoelectric resonator, a piezoelectric oscillator and the like, have been widely used for small information equipment, such as hard disc drives (HDDs), mobile computers, and integrated circuit (IC) cards, and for mobile communications equipment such as mobile phones, car-phones, and paging systems, and piezoelectric gyro sensors, etc.
FIG. 17 is a schematic plan view illustrating an example of a piezoelectric resonator element conventionally used in the piezoelectric devices.
In FIG. 17, a piezoelectric resonator element 1, whose shape shown in the figure is formed by etching a piezoelectric material such as quartz or the like, is provided with a base 2, which is mounted to a package (not shown) or the like, and has a rectangular shape, and a pair of vibration arms 3 and 4, which extend from the base 2 in the vertical direction in FIG. 17. Long grooves 3a and 4a are formed on the main surfaces (front and back surface) of the vibration arms, and necessary driving electrodes are formed.
In the piezoelectric resonator element 1, when a driving voltage is applied via a driving electrode, the vibration arms 3 and 4 perform a flexural vibration so that their distal parts move closer and then spread apart, resulting in an output signal having a given frequency.
Here, the piezoelectric resonator element 1, in which lead-out electrodes are formed at the positions indicated at numerals 5 and 6 on the base 2, is fixed to a base substrate such as a package or the like with adhesives 7 and 8 applied on the lead-out electrodes.
After fixing and supporting the piezoelectric resonator element 1 with the adhesive, cut parts 9 are formed in the base 2 so that the flexural vibration of the vibration arms is prevented from being hindered by remaining stress caused by the differences in the linear expansion coefficient between the material of the package or the like, and the material of the piezoelectric resonator element.
In the piezoelectric resonator element 1, as a result of miniaturization, the width W1 of each of the vibration arms 3 and 4 is approximately 100 μm, the distance MW1 between them is approximately 100 μm, and the width BW1 of the base 2 is approximately 500 μm. These parts are miniaturized, so that the length BL1 of the base is accordingly shortened. As a result, the piezoelectric resonator element 1 is miniaturized.
See JP-A-2002-261575 for an example of this related art.
However, the piezoelectric resonator element 1, which is miniaturized, has the following problem in its temperature characteristics.
FIGS. 18 and 19 are graphs illustrating the temperature characteristics of the piezoelectric resonator element 1. FIG. 18 shows a temperature-frequency characteristic. FIG. 19 shows a temperature-crystal impedance (CI) value characteristic.
As shown in the figures, the temperature-frequency characteristic shown in FIG. 18 shows no problem. However, the temperature-CI value characteristic shown in FIG. 19 has a problem in that it is highly unstable.
It can be considered that the deterioration of the temperature-CI characteristic occurs due to the change of the stress condition at the positions of the base 2 in the piezoelectric resonator element 1, which are bonded with the adhesives 7 and 8, by temperature change. Similar influences can occur due to the change of the stress condition at the positions of the base 2, which are bonded with the adhesives 7 and 8, when they are affected by drop shock or the like.